Transformer



April 12, 1938- c. w. KRONMILLER TRANSFORMER Filed Oct. 15, 1937 ,8- Invefi Charles W K1OT'mniHr-JP b9 x wmyfjmdbm His Attovney.

Patented Apr-.12, 193s UNITED STATES MSIOIIEB M W. Kromniller. Fort Wayne, Ind, assignor to General Electric Company, a corporation of New York Application October- 15, 1031. Serial No. 109,15:

2 Claim. (01. 111-119) My invention relates to transformers. The load circuit of a transformer is often of such character that the current supplied by the secondary winding of the transformer contains many high harmonics which may induce similar high harmonics in the primary circuit of the transformer throughboth the electromagnetic and electrostatic coupling between the two winding's. These high harmonics in the primary circult of the transformer are objectionable because they are apt to cause serious radio disturbances even at considerable distances from the transformer. A common example of transformer load in which these high harmonics appear is an ignition circuit for oil burners used in heating plants. The spark or are which ignites the oil is responsible for the high harmonics in the secondary winding of the transformer and if these high harmonics are permitted to induce similar harmonics in the primary winding they will spread through the entire primary circuit and cause serious radio disturbances for considerable distances.

One object of the invention is to provide an improved conductive shield between the two windings of a transformer to protect the primary winding and primary circuit of the trans former from high frequency disturbances in the secondary winding. A further object of the invention is to provide the transformer with a protective casing and to arrange the conductive shield to form a partition within the casing and so to divide the interior of the casing into separate high voltage and low voltage compartments for the two windings.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which Fig. l is a perspective view of an encased transformer constructed in accordance with the invention; Fig. 2 is a sectional view of the transformer on the line 22 of Fig. 4; Fig. 3 is an exploded view.

of the transformer and its casing; Fig. 4 is a sectional view of a portion of the transformer and its casing on the line 44 of Fig. 2; and Fig. 5 is a perspective view of the conductive shield which is used between the two windings of the transformer and which divides the casing into the two separate compartments. 50 The transformer ill, shown most clearly in Fig. 3, includes a magnetic core ll having a winding leg l2 and two outer legs i3 and I4. The winding leg I2 is surrounded by a low voltage primary winding IS and a high voltage sec- 55 ondary winding ii, the secondary winding being terminals H of the transformer.

shown as including two sections or coils which may be connected in series between the secondary The transformer is of the high reactance type and includes magnetic shunts ll between the two windings to divert more and more of the primary magnetic flux from the secondary winding as the load increases so that a relatively high voltage is available to start the secondary current but so that the secondary voltage and current are limited to safe values after the current starts. A conductive shield is in the form of a flat metal plate or sheet isdisposed between the primary winding l5 and the secondary winding l6 and magnetic shunts It. This conductive plate is preferably formed of magnetic steel but may be of any suitable conductive metal such as copper or aluminum. The shield i9 is disposed around the winding leg l2 but is formed with a short gap 20 which is provided so that the shield cannot form a short-circuited turn around the winding leg I! of the transformer.

The transformer i0 is enclosed in a suitable metallic casing 2l provided with an insulating bushing 22 for the primary connections 23 and insulating bushings 24 for the high voltage secondary leads 25, the secondary leads 25 being of course connected to the secondary terminals II.

The shield l9 extends beyond the transformer II itself to fit substantially across the interior of the transformer casing 2i and form a partition dividing the interior of the casing into a low voltage compartment 26 and a high voltage compartment 21, the low voltage compartment 26 containing the low voltage primary winding l5 and its connections 23 and the high voltage compartment 21 containing the magnetic shunts l8 and the high voltage winding 16 with its connections 25. The high voltage compartment 21 may be filled with an insulating compound, as indicated in Fig. 4. The casing 2i may be provided with a removable cover plate 28 to permit convenient access to the low voltage compartment 26 wherein connections may be made between the low voltage leads 2!! of the primary winding and the outside primary conductors 23. It is not necessary of course that the shield l9 fit tightly within the casing 2| but it should fit tightly enough to protect the low voltage winding l5 and its connections from the high voltage winding l5 and its connections and to confine the insulating compound surrounding the high voltage secondary parts to the high voltage compartment 21 in case such compound is provided. It has been found that a shield I9 formed of magnetic material has some advantages over a shield formed of non-magnetic metal in that a magnetic shield acts as a magnetic shunt between the two windings II and I and so permits the use of a correspondingly smaller amount of ma netic material in the magnetic shunts II. In order that it may act most eifectively as a shield, the shield is should be connected conductively to ground, as indicated by the soldered connection 30 shown in Fig. 3, the core II and casing of course being usually grounded while the transformer is in service. The shield ll which has been described is of particular advantage in that it effectively shields the primary winding II and its connections from high frequency disturbances in the secondary winding and further provides a useful partition within the casing so arranged that the low voltage parts of the transformer are effectively protected from the high voltage parts and any insulating compound surrounding the high voltage parts is coniined to those parts and cannot reach the low voltage leads and interfere with their connection to the outside conductors 23.

' The invention has been explained by describs ing and illustrating a particular arrangement of encased transformer and conductive shield, but it will be apparent that changes may be made without departing from the spirit of the invention and the scope of the appended claims.

whatlclaimasnew anddesiretoseeureby Letters Patent of the United States. is:-

1. A transformer including a magnetic core having a winding leg, primary and secondary windings surrounding the winding 16!. a magnetic shunt between the windings for diverting magnetic flux from the secondary winding, a conductive shield disposed around the winding leg between the primary winding and said secondary winding and shunt, and a casing enclosing the transformer, the shield extending to form a-partition dividing the casing into two compartments with the primary winding in one compartment and the secondary winding and shunt in the other compartment.

2. A transformer including a magnetic core having a winding leg. primary and secondary windings surrounding the winding leg, a magnetic shunt between the windings for diverting magnetic flux from the secondary winding, a shield of magnetic material disposed around the winding leg between the windings, and a casing enclosing the transformer, the shield extending to form a partition dividing the casing into two compartments with the primary winding in one compartment and the secondary winding in the other compartment.

CHARLES W. KRONMILLER. 

